This invention relates generally to piezoelectric devices. As used herein, a piezoelectric device includes piezeoelectric resonators, filters and surface acoustic wave (SAW) devices. More specifically, this invention is directed to a piezoelectric device disposed in a two piece package which is sealed together to form a hermetic seal. This invention also addresses the problem of making electrical connections with the piezoelectric device through the package, commonly referred to as "feed-through" connections.
Quartz crystal resonators have been used for many years as the frequency controlling element in an oscillator circuit. Because of environmental considerations often associated with electronic equipment and computers, it is usually desirable to protect the crystal resonator within a hermetically sealed package.
One commonly used quartz resonator package consists of a header and a metal container which is sealed to the header. The header consists of a metal frame, a sealing glass contained within the frame, and Kovar pins which pass through the glass to provide electrical connections to a quartz resonator mounted inside the sealed package. These pins and the sealing glass are selected to have generally similar thermal expansion properties so that a hermetic seal of the package is maintained over an operating range of temperatures. While this package has generally proved successful, there exists a demand for a quartz resonator package which can be readily manufactured and more easily handled in accordance with modern manufacturing techniques. For example, a leadless hermetically sealed resonator which could be easily mounted to a printed circuit board by an automatic machine would be desirable.
Various types of resonators with glass containers have been suggested; for example, see U.S. Pat. Nos. 4,293,986, 4,362,961, 4,445,256. The packages disclosed in these patents comprise two halves which are made of glass, or glass and ceramic, and have a recess in one half for receiving a quartz resonator. Such glass packages are bonded together about their periphery by means of a eutectic metal, such as solder. A hermetic seal is formed about the periphery of such a package due to the melting of the deposited eutectic material. However, depositing a eutectic material having a relatively low melting point about the periphery of each half of the glass package may require an intermediate layer of a different material since the desired eutectic material may not directly adhere to the glass.
A significant consideration with respect to a hermetically sealed crystal package is the means by which electrical connections can be brought outside the package while still maintaining the integrity of the hermetic seal. While it is apparent that holes can be formed in the walls of a package, providing a hermetic seal which can be easily and reliably manufactured to permit electrical connections to be made through the hole presents a difficult problem.